1. Technical Field
The invention relates to a diagnostic tool for non-invasively detecting when a spark plug ignition system fires and to provide a visual or audio indication of such firing. More particularly, the invention relates to such a diagnostic tool which uses an antenna to pickup or detect the electric field generated by a component of an ignition system during firing to provide a visual or audio firing indication eliminating the heretofore spark plug firing indicator using a metallic contact and a neon indicating tube or lamp.
2. Background Information
The prior art of spark plug firing indicators and ignition system testers is comprised of devices which use neon lamps or neon tubes that act as both firing detectors and firing indicators using a single lamp or tube.
When a firing voltage is generated by an ignition system, an electric field develops around the spark plugs, spark plug wires, and the secondary of the ignition coil. The electric field can directly ionize inert gas contained in a neon tube if the tube is placed directly in the field. Such is the principle of operation of neon-type spark plug and ignition system diagnostic tools which have worked very well in the past.
One disadvantage of the neon-type tools is that the duration, and ultimately the brightness, of the flash or glow of the neon gas, is directly related to the duration of the electric field surrounding the device. Short duration firing sequences cause short duration flashes which are difficult to see. Furthermore, because the flashing and pickup characteristics of the neon tube are based on the physical properties of the gas in the enclosed tube, there is no mechanism for any kind of user sensitivity adjustment. This can be a disadvantage when trying to diagnose problems with the many different ignition systems made by different manufacturers.
Modern engines and ignition system components have changed from past models to such a degree that the neon-type tools now produce a flash that's very difficult to see. This makes the tools almost useless for today's diagnostic technician. Changes in high-energy ignitions, higher dielectric strength spark plug wires, shorter duration firing voltages, and solid-state distributors are all contributing to help make the neon-type tools obsolete.
The present invention provides two primary functional advantages over neon-type and similar ignition system diagnostic tools.
The first advantage involves the detection of the electric field generated by the firing voltage of an ignition system. The present invention uses an antenna to non-invasively pick up the electric field and uses solid-state circuitry to compare its strength with a variable sensitivity threshold. Once the threshold is reached or exceeded, part of the circuit generates an indication to the user. The variable sensitivity and solid-state nature of the tool, compared to the fixed and often erratic sensitivity of a neon-type tool, provide more accurate and repeatable readings.
The second advantage involves the use of electronic circuitry to generate a firing indication that is independent of the duration of the firing voltage. During the firing of a spark plug, for example, if the firing voltage is only present for tens of microseconds, an indication signal will still be present for many thousands of microseconds. The circuit generated extended time period of the indication signal allows a user to detect short duration firings for accurate diagnostic troubleshooting.